The present invention relates to an extrusion process for the manufacture of cooked cereals or dry pet food, an apparatus for carrying out the process and a product obtainable by the process.
U.S. Pat. No. 5,997,934 (Geromini et al.) discloses a process for the manufacture of cooked cereals or dry pet food which comprises preparing a mixture of water and a dry premix mainly comprising cereal flour or semolina, cooking the mixture and extruding it by pressing it through an extrusion die with the aid of a gear pump.
U.S. Pat. No. 5,667,833 (Juengling et al.) discloses a process and an equipment for manufacturing pasta which comprises preparing a mixture of cereal flour and water having a water content of 25-40%, kneading the mixture and extruding it by pressing it through an extrusion die with the aid of a gear pump.
It would be desirable to provide an extrusion process and apparatus which maintains the molecular structure of the starch in order to manufacture a product with properties that are close to those of a traditional roller-dried product but superior to those of a traditional cooked-extruded product.
As a matter of fact a traditional roller-dried product was not subjected to any mechanical stress during its entire manufacturing process, because a traditional roller-dried product was obtained by roller-drying a cooked slurry mainly comprising cereal flour and 40-45% water, with the slurry having been cooked in a vat and the drying effect being obtained by pure heat transfer from the roller to the film of slurry applied on its surface.
On the other hand, a traditional cooked-extruded product was subjected to high shear during its manufacturing process, because it was subjected to high pressure and friction while being cooked in the extruder.
The process of Geromini et al. mentioned above in fact comprises extrusion-cooking the mixture of water and flour before pressing it through an extrusion die with the aid of a gear pump.
On the contrary, the whole process of Juengling et al. mentioned above is carried out while maintaining the temperature of the mixture of water and flour or semolina below 55° C. so that a raw pasta is obtained, without any gelatinization of the flour or semolina. Neither process can accomplish the desired objectives.
In view of these deficiencies of the prior art, there is a need for improved processes and products with improved properties, and these are now provided by the present invention.